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Monarch Butterfly Migration Update: March 14, 2001

Today's Report Includes:

Have the First Migrants Reached Texas?

First Monarch Migration Map of Spring, 2001

As today's map shows, recent sightings in Texas may indicate the arrival there of the first migratory monarchs from Mexico!

The first inland sighting in Texas, over 130 miles west of the Gulf Coast, occurred on March 3rd:

March 3 Catarina, TX (28.31N, -99.49W)
"Adult monarch seen during the late afternoon on 3/3/01 flying low through mixed brush."

The Aschens, who have been carefully monitoring monarchs on the Gulf Coast all winter, noticed directional flight by a monarch they saw last Friday:

March 9 Victoria, TX (28.81N, -96.98W)
"At three this afternoon, we were driving along a narrow lane just east of Victoria when we sighted a monarch just ahead, flying parallel to us from the southwest to the northeast. This might be the first monarch we have seen from Mexico and not one of the overwintering coastal monarchs. It was quartering into a light north breeze from the Pacific front that moved through last night." (

If you live in Texas or the other Gulf States, please keep your eyes on the skies--and be ready to report monarchs! Also watch for signs of the first monarch eggs and larvae.

Your observations are VERY important! Scientists have many questions about the population of monarchs that overwinters along the Gulf Coast, in locations shown in red on today's map. For example, do these butterflies breed all winter and then become migratory in the spring? With enough data, our study may shed light on the timing and patterns of monarch migration in the south in spring.

Milkweed Emerging on the Migration Trail
This map shows where observers have reported milkweed emerging so far this spring:

Please report the FIRST MILKWEED to Emerge This Spring!

We hope you will help us monitor the spring emergence of the monarch's food plant across North America.

Field Notes from the Mexican Monarch Sanctuaries
by Dr. Bill Calvert

March 12, 2001
The snow is gone from nearly everywhere but the highest elevations. Since it never became very cold following the storm, most of the butterflies were spared. (It's during the cold, clear nights after a storm that wet butterflies are particularly susceptible to freezing.)

If the clear weather persists tomorrow when we visit Rosario we can expect a butterfly blizzard. Warm, clear weather stirs butterflies up to a frenzy. There is much movement of the colonies downslope. Many millions fly through the woodlands each day to take water and nectar, and perhaps to exercise their wing muscles in preparation for their return migration to the north.

Millions of Monarchs Eaten Each Year by Predators
Before the monarchs arrived here in November, there was not a single butterfly wing on the ground. At the end of the season in March, the forest floor is peppered with dead butterflies. In a typical year, we estimate upwards of 12-15% of the entire over-wintering population dies due to predatory activities. Millions of monarchs clustered together are a rich source of food--and easy prey. But only for those predators who can successfully eat monarchs.

There are 3 main monarch predators in the sanctuary, one mouse species and two bird species. Close inspection of a dead butterfly gives a clue as to its predator:
Predator Clue
Black-headed Grosbeak The monarch's abdomen is entirely missing.
Black-backed Oriole The monarch's abdomen is present, but it appears to be "unzipped" (slit open) and the thorax is gorged.
Black-eared Mouse Caches of butterflies are found on the ground, and only the wings remain.

Challenge Question #13
Who Ate These Butterflies?

Inspect these butterflies carefully and see if you can determine who the predators were:
(Click on photos to enlarge.)




(To respond to this question, please follow the instructions below.)

Increased Mating Signals End of Wintering Season
Because their lives will soon end, the monarchs must now prepare to
pass their genes to the next generation. Mating increases as the over-wintering season draws to a close. In late February, for example, one might see 5 or more mating attempts in a 10 X 10 foot area. Of these, only about 1 in 10 pairs actually join to mate. Most pairs (90%) break apart just as they strike the ground.

By mid-March, mating attempts and successes have increased dramatically. Where 1-5 mating pairs could be seen at one time in the trails below the colonies, we'll now see three times as many mating pairs leading up to the monarchs' departure.

Mating proceeds like this: A male patrolling the canopy grasps the wings of a female, using the claws on his feet as he encounters her. The pair parachutes down to the ground. If he manages to attach to her (about 10% of the time), she folds her wings and he then flies off with her, if he can, to a safe perch where mating is completed.

Next week will be my last week here for the season, so I'll phone in one more report.

Until then,
Bill Calvert
Recommended Web Site:
Monarch Butterfly Nuptial Flight Research

An interdisciplinary team at Cal Poly is studying the nuptial flight of monarchs. Be sure to visit this site which includes movie clips of the monarch's nuptial flight!

Bienvenidos al tiangis en Angangueo!
"Welcome to the Market in Angangueo! It's 9:01 a.m. Monday morning, and along every winding street, at every town corner and in all the store windows you find customers and merchants from near and far. They have all set aside the entire day to exchange goods for pesos. Many of the delights found at the tiangis (a large community market, usually held weekly on a designated day of the week) can be seen as we wander through the streets and among the vendors of Angangueo.

"At the end of the day, join the parade as hundreds of campesinos return to their homes in the surrounding mountains, traveling by foot and donkey, laden with the day's treasures. Leading the pack are the young and energetic, typically boys running up the steep hillside with their donkeys, followed by girls walking and talking with their friends. Then come the men, usually carrying a heavy load. Much later come the mothers with small children. And, at the end of the trail, come the elderly who are tired but happy to continue the weekly tradition of a trip to town."

  • How many students in your class would like to have their own donkey--and take it shopping instead of driving in a car?
  • Now that the monarchs are about to leave Mexico, think about all you've learned about the people there. What aspects of their lives interest you the most? What would be most difficult?

Link to Collection of Bilingual Vignettes
Life in the Sanctuary Region

You'll find a total of 12 bilingual vignettes, including the following which have not been highlighted this spring:
  • A Walk Through the El Rosario Monarch Sanctuary With Guide Javier
  • Orelia Moreno Shares Life on an Ejido
  • A Glimpse of Daily Life in Garatachea - A Report from Naomi
  • Tortillas From Scratch - Making Tortillas With Maria Luis
  • The Indigenous Community of Mazahua - Going Back in Time with Mala

How to Respond to Today's Challenge Question:

1. Address an e-mail message to:
2. In the Subject Line of your message write: Challenge Question #13
3. In the body of your message, answer the question above.

The Next Monarch Migration Update Will Be Posted on March 21, 2001

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